Bisphenol A [2,2-bis(4-hydroxyphenyl)propane] is known to be an important compound for a material for engineering plastics such as polycarbonate resin and polyarylate resin or for epoxy resin, and there is increasing a great demand for it these days.
It is known that bisphenol A is produced by condensing acetone and excess phenol in the presence of an acidic cation-exchange resin catalyst and optionally a sulfur compound promoter such as alkylmercaptan. In the process, the acidic cation-exchange resin catalyst degrades with time. A principal cause of the catalyst degradation is the heavy material derived from the starting compounds, and the catalyst begins to degrade first around the inlet port of the reactor. Since its degradation speed is high, an excess amount of the catalyst is charged into the reactor for long-term continuous operation for bisphenol A production. After the catalyst has begun to degrade, the amount of acetone to be fed into the reactor must be time-dependently increased for keeping the product yield (that is, for keeping the intended degree of phenol conversion). In that case, the non-reacted acetone that goes out of the reactor is recovered in the distillation column connected to the outlet port of the reactor. Therefore, the amount of acetone that maybe increased in the process is limited by the capacity of the distillation column. That is, at the limit of the capacity of the distillation column, the catalyst in the reactor is exchanged with a fresh one. Accordingly, if the reaction condition could be suitably controlled so as not to increase the amount of acetone and so as to use the catalyst as long as possible in the reactor, it will reduce the production costs. In this connection, some patent applications relating to improvement of the reaction condition have been laid open to public inspection, though their objects differ. For example, Japanese Patent Laid-Open No. 19952/1979, Japanese Patent No. 2,779,952, Japanese Patent Laid-Open No. 246458/1999 and U.S. Pat. No. 4,400,555 disclose a specific arrangement of reactors connected in series in which a carbonyl compound divided into some portions is added separately to each reactor. In these, however, there is still room for improvement for prolonging the life of the acidic cation-exchange resin used.
The present invention has been made in consideration of the above-mentioned matters, and its object is to provide a process for producing bisphenol A in which the life of the catalyst, acidic cation-exchange resin used can be prolonged.